Antenna reflector



' June 12, 1951 J, MAS 2,556,969

ANTENNA REFLECTOR Filed April 5, 1946 lNVENTOR SAMUEL J. MASON ATTORNEY radar.

Patented June 12, 1951 ANTENNA REFLECTOR Samuel J; .Mason, Boston, Mass.. assignor, by

mesne assignments, to the United States of America as represented by thesecretary of the Navy Application-April 5, 1946, Serial- N 0. 659,712-

/, -8 Claims. (01. -25.033.65)

This invention relates to reflectorstfor reflecting electromagnetic radiation and more particularly to sectional paraboloidal reflectors with specially shaped peripheries for use with surface sear'chra'dar antennas.

For surface search radar it'is desirable .to concentrate the radiation from the antenna into as small a sector'of azimuth as possible in order to secure good definition of targets :andt'for high resolving power to distinguish between closely spaced targets; Any appreciable radiation in other than. the selected azimuthiis undesirable since it. introduces false target indications on the These undesirable secondary radiations occur with ordinary parabo'loidal'reflectors and they are referred to as side lobes. For surface search radars, these side lobes are troublesome only when they occur in the azimuth radiation pattern. Azimuth side lobes maybe caused :by diffraction of waves reflected from the paraboloidal reflector, or dish 'by diffraction of waves emerging fromithe dish'by a horn or'other feed obstructing them; or by direct radiation from the feed.

The general object of the present invention is to provide a novel sectional paraboloidal antenna reflector which will reduce undesired side lobe radiation to a minimum.

Another object of the present inventionv is to provide a sectional paraboloidal reflector with a specially shaped periphery to secure low side lobe radiation in the azimuth pattern.

A further object of. the :present invention is to provide a novel sectional paraboloidal reflector with asymmetricv feed to secure low side lobe radiation in the azimuth pattern.

These and other objects will, be apparent from the '"following specification when taken with the accompanying drawings'inwhich:

Fig. 1 is a perspective view of one embodiment of the invention as applied to a surface search radar antenna.

Fig. 2 is a front View of the embodiment shown in Fig. 1.

Fig. 3 is a side view in partial section along the line III-III of the embodiment shown in Fig, 1. Referring to Figs. 1, 2, and 3, a reflector, or

dish II, has its periphery shaped as shown, the

first plane. That is to say, such .a paraboloidal each other ina point at the opposite extremities thereof. The lateral. distance from extremity I2 to extremity l3 is'substantially twenty (20) wavelengths of the radiationrwith which the antenna is used. The internal reflecting'surface of dish I! is curved "to formza paraboloid whose focus is :at point M which :also coincides with the'opening 10f an electromagnetic horn l5. Horn [5 is attached to a wave guide Itwhichserves to guide the-radar energy between the radar set and the antennadish ll. The-purpose'of'horn E5 on the end of wave guide i6 is to match; the impedance of said wave guide [6 to the impedanceof space thereby providing for efficient transfer of energy, and its construction follows conventional wave guide design. Horn l5 has its axis ['7 inclined to the-horizontal .at an angle a but the plane of the openinng I4 of said horn i5 is vertical. Radiation follows axis :1! and is reflected by the 25 dish H along a path [8 abovethe horn l5.

Bearing-in mind the three-previously mentioned causes of side lobe radiation, it can readily be understood that the special shape of the dish periphery operates to reduce-side lobe radiation ,dueto diffraction of waves reflected from the dish; placement of the horn opening I' l below theradiated beam !*8- operates tozlimit side lobe radiation due to diffraction of waves emerging from the dish H "by the-horn feed i5; and the construction .of the horn opening M so that its plane is not; normal to thehornaxis lJ'i' operates "three o'f thecausesof side lobe radiation from a paraboloidal reflector, a novel antenna system relatively free from troublesome side lobe radiation in the azimuth pattern results.

What is claimed is:

1. A reflector for reflecting radio microwave radiation comprising a paraboloidal section formed by passing a plane parallel to the axis of generation of a paraboloid intersecting the surface of said paraboloid and by passing a second plane at an acute angle to said first plane intersecting the surface of said paraboloid, the lines of intersection of said planes with the surface of said paraboloid defining the opposite longitudinal edges of said reflector.

2. A reflector for reflecting radio microwave radiation comprising a paraboloidal section formed by passing a plane parallel to the axis of generation of a paraboloid intersecting the surface of said paraboloid and by passing a second plane at an acute angle to said first plane intersectin the surface of said paraboloid, the lines of intersection of said planes with the surface of said paraboloid defining the opposite longitudinal edges of said reflector, the open ends of said longitudinal edges each intersecting in a point.

3. A reflector comprising a paraboloidal section formed by passing a plane parallel to the axis of generation of a paraboloid intersecting the surface of said. paraboloid and by passing a plane at an acute angle to said first plane intersecting the surface of said paraboloid, the upper and lower edges of said paraboloidal section intersecting each other in a point at the opposite extremities thereof.

4. An antenna for radio frequency radiation comprising a paraboloidal section reflector formed by passing a plane parallel to the axis of generation of a paraboloid intersecting the surface of said paraboloid and by passing a second plane at an acute angle to said first plane intersecting the surface of said paraboloid, the lines of intersection of said planes with the surface of said paraboloid defining the opposite longitudinal edges of said reflector; and an electromagnetic feed horn having its opening coinciding with the focus of said paraboloid, the axis of said horn being inclined to the axis of said paraboloid, said axis of said horn pointing substantially at the center of said paraboloidal section, and the plane of the opening of said horn being perpendicular to said axis of said paraboloid.

5. A reflector comprising a conductive, paraboloidal section formed bypassing a plane parallel to the axis of generation of a paraboloid intersecting the surface of said paraboloid and by passing a second plane at an acute angle to said first plane intersecting the surface of said paraboloid, said planes being so positioned with respect to said axis of generation that the major portion of said section lies on one side of said axis of generation, the upper and lower edges of said paraboloidal section intersecting each other in a point at the opposite extremities thereof.

6. A reflector comprising a conductive paraboloidal section formed by passing a plane parallel to the axis of generation of a paraboloid and at a predetermined distance from said axis, intersecting the surface of said paraboloid, and by passing a second plane at an acute angle to said first plane intersecting the surface of said paraboloid, said planes being taken such that substantially all of said section lies on one side of said axis, the upper and lower edges of said paraboloidal section intersecting each other in a point at the opposite extremities thereof.

'7. An antenna for radio frequency radiation comprising a conductive paraboloidal section formed by passing a plane parallel to the axis of generation of a paraboloid and at a predeter mined distance from said axis intersecting the surface of said paraboloid, and by passing a second plane at an acute angle to said first plane intersecting the surface of said paraboloid, said planes being taken such that substantially all of said section lies on one side of said axis, the lines of intersection of said planes with the surface of said paraboloid defining the opposite longitudinal edges of said reflector, said edges meeting in a point at opposite extremities of said section and an electromagnetic feed horn having its opening coinciding with the focus of said paraboloid, the axis of said horn being inclined to the axis of said paraboloid and pointing substantially at the center of said paraboloidal section, the plane of the opening of said horn being perpendicular to said axis of said paraboloid, said horn lying in the plane perpendicular to said first mentioned plane that includes said axis, said horn being further positioned on the side of said axis opposite the major portion of said paraboloidal section.

8. An antenna for radio frequency radiation comprising a paraboloidal section reflector formed by passing a plane parallel to the axis of generation of a paraboloid, said plane intersecting the surface of said paraboloid, and by passing a second plane at an acute angle to said first plane, said second plane intersecting the surface of said paraboloid, the lines of intersection of said planes with the surface of said paraboloid defining the opposite longitudinal edges of said reflector; and an electromagnetic feed horn having its opening coinciding with the focus of said paraboloid, the axis of said horn ponting substantially at the center of said paraboloidal section.

SAMUEL J. MASON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,281,274 Dallenbach et al. Apr. 28, 1942 2,283,935 King M May 26, 1942 2,407,068 Fiske et al Sept. 3, 1946 FOREIGN PATENTS Number Country Date 436,355 Great Britain Oct. 9, 1935 

